Human cytomegalovirus (CMV) is a ubiquitous agent in human populations. Infections are generally asymptomatic, but there can be serious medical manifestations of the disease in immunocompromised individuals (transplant recipients and AIDS patients) and in congenitally infected newborns. In immunodeficient patients, primary CMV infection and reactivation of latent virus is associated with serious disease including retinitis and pneumonia. CMV infection also predisposes the patient to fungal and bacterial infections. Congenital CMV infection of the fetus occurs in about 1% (36,000) of infants born in the U.S. per year. Of these infants 10-20% will have symptomatic infection at birth or within two years of birth with a mortality rate of 10-15%. Among the survivors, many will have mild to severe neurologic complications including hearing loss, learning disabilities and mental retardation.
Vaccines that prevent or reduce CMV-associated disease are clearly needed. The CMV (Towne) strain has been tested as a vaccine candidate in normal individuals and renal transplant patients (Quinnan, Jr., G. V. et al. (1984) Am Intern Med 101:478-483); (Plotkin, S. A. 1985, CMV Vaccines, In: The Herpes Viruses vol. 4, ed., Roizman and Lopez, Plenum Press, N.Y., p. 297-312). While this vaccine appeared to have no deleterious effects and did reduce symptoms of CMV disease in transplant recipients, there are many objections to the use of experimental live attenuated virus vaccines, including the possibility of immune impairment resulting from virus infection and reports of possible association between CMV and oncogenesis.
In the absence of a complete understanding of the biology of CMV, the most rational approach to a vaccine would involve the development of subunit vaccines based upon the surface glycoproteins of the virus using recombinant viral glycoproteins which elicit neutralizing antibodies.
Like other herpesviruses, CMV specifies multiple glycoproteins (Stinski, M. (1976) J Virol 19:594-609; Pereira, L., et al. (1982) Infect Immun 36:933-942). Characterization of these have involved studies of CMV-infected cells and purified virions using polyclonal and monoclonal antibodies (Pereira, L., et al. (1984) Virology 139:73-86; Britt, W. J. (1984) Virology 135:369-378; Nowak, B., et al. (1984) Virology 132:325-338; Law, K. M., et al. (1985) J Med Virol 17:255-266; Rasmussen, L., et al. (1984) Proc Natl Acad Sci USA 81:876-880; and Britt and Auger (1986) J Virol 58:185-191).
U.S. Pat. No. 4,689,225, issued 25 Aug. 1987 and based upon the work described in the Pereira et al. references, supra, describes a method and vaccine for CMV infections using a polypeptide designated therein as glycoprotein A (gA1-A7) of cytomegalovirus. Two glycoproteins designated p130 (gp130) and p55 (gp55) (based on the molecular weights given in kilodaltons) have been partially purified and shown to elicit a neutralizing response in guinea pigs (Rasmussen, L., et al. (1985) J Virology 55:274-280). The gp130 glycoprotein appears to be a precursor to the gp55 glycoprotein.
The gB gone from CMV strain AD169 (which appears to be similar to the p130 CMV protein described by Rasmussen et al., supra) has been identified by nucleotide sequencing (Cranage, M. P. et al. (1986) EMBO J 5(11):3057-3063) with a 906 amino acid protein deduced therefrom. The gB gene product was expressed in recombinant vaccinia virus and rabbits immunized with this gene product produced antibodies that immunoprecipitate gB from CMV-infected cells and neutralize CMV infectivity in vitro (See also WO 87/05326).
Although there is much ongoing activity towards both the identification of major glycoproteins which are the targets for viral neutralization and the development of a subunit CMV vaccine, to date, the origin of the gp55 CMV glycoprotein has not been established nor has gp55 been identified by nucleotide or amino acid sequence and therefore, no vaccine composed of the 55,000 dalton recombinant viral gB protein or any truncated recombinant polypeptide thereof has been reported. Clearly, in light of the absence of a complete understanding of the biology of CMV, it would be desirable to provide a safe, effective and economic vaccine capable of affording protection against cytomegalovirus infections, as well as to provide diagnostic reagents capable of detecting the particular immunogenic stimulus resulting from CMV infections.